The biological mechanisms by which the plaque and crevicular flora cause periodontal disease are being studied. Mechanisms of bone loss specifically are studied in a bone-tissue-culture model. Effects of both bacterial products (endotoxins, lipoteichoic acids, etc.) and immunological mediators are being tested. An animal model (Macacus speciosa) whose bacterial flora and periodontal tissues closely resemble those of man is used to study the inflammatory phase of disease. This involves identification of bacterial antigens and products which interact with host immune systems or directly affect host tissues. When it becomes appropriate, studies will be extended to humans. The long-term goal is to secure information which can be used in the diagnosis, prevention and treatment of alveolar bone loss in human periodontal disease.